Method for processing a sample

ABSTRACT

A method for processing samples in a sealable container which is transparent to electromagnetic radiation, includes a) the sample and a polar non-solid medium being introduced into the container, b) the container being placed in a vessel which is transparent to electromagnetic radiation and which is filled with a nonpolar coolant which is transparent to electromagnetic radiation, and c) the vessel being irradiated with electromagnetic radiation, the temperature of the coolant being maintained lower than 5° C. and a vessel being used which is provided with an insulating material which is transparent to electromagnetic radiation.

BACKGROUND OF THE INVENTION

The invention relates to a method for processing samples in a sealablecontainer which is transparent to electromagnetic radiation, in whichmethod;

a) the sample and a polar non-solid medium are introduced into thecontainer.

b) the container is placed in a vessel which is transparent toelectromagnetic radiation and which is filled with a nonpolar coolantwhich is transparent to electromagnetic radiation, and

c) the vessel is irradiated with electromagnetic radiation.

A polar non-solid medium is understood as meaning a medium which is inthe liquid state when it is used. It is therefore possible that thepolar non-solid medium is in the solid state at fairly low temperatures,for example at room temperature, but the polar-non-solid medium becomesliquid at higher temperature.

DESCRIPTION OF THE RELATED ARTS

The French Patent Application 2,674,146 discloses a device whichcomprises a cylindrical outer container and a cylindrical innercontainer. The outer container comprises a vessel and a lid which aredetachably joined to one another. The lid of the vessel is provided witha plunger which, when the lid and the vessel of the outer container arejoined to one another and the inner container is placed in the outercontainer, seals the inner container. Both the inner container and theouter container are essentially transparent to microwaves and the outercontainer is resistant to high pressure. Furthermore, a space is presentbetween the outer container and the inner container into which a coolantcan be introduced. The coolant is preferably air, but can also beanother gaseous or liquid substance, provided that said substance absorbhas little or no microwave absorption. The device according to theFrench Patent Application 2,674,146 is said to be suitable, inparticular, for heating substances under high pressure using microwaves.A disadvantage of said device is, however, that, if a coolant is usedwhich is at a low temperature, for example solid carbon dioxide orliquid nitrogen, condensation of water vapour on the outside of theouter container will occur. This condensed water vapour will absorbmicrowave radiation during the heating, as a result of which the heatingof the substances which are present in the inner container cannot beadequately effected.

It is known that samples, for example soil samples, often have toundergo a processing before the samples are suitable for chemical andphysical analyses. Thus, soil samples, for example, are treated with amixture of concentrated nitric acid and concentrated hydrochloric acid(aqua regia) to dissolve heavy metals present in the sample. Aqua regiais added to such samples and the mixture obtained in this way is heatedfor a certain time. The treatment is carried out by introducing thesample and the aqua regia into a sealable container which is transparentto microwave radiation. The mixture of the sample and the aqua regia isthen heated by exposing the container to microwave radiation. Then thecontainer has to be cooled and the sample has to be subjected to furthertreatment, such as weighing, decanting, filtering, centrifuging anddiluting, after which the contents of heavy metals dissolved in the aquaregia are determined. A disadvantage is that the container has to bemade of Teflon. It has been found that such containers have to bevigorously and thoroughly cleaned before re-use, in particular if thecontainers contain chemically aggressive substances, such as aqua regia.

SUMMARY OF THE INVENTION

The present invention has the intention of providing a solution to theproblems and disadvantages cited above. The object of the invention isto provide a method for treating samples, in which method the containerno longer has to be cooled after the small vessel has been exposed tomicrowave radiation. Another object of the present invention is toprovide a method in which the further processing steps, such asweighing, diluting and the like, are no longer necessary. A furtherobject of the present invention is to provide a method which can also becarried out on a small scale, as a result of which less chemical wasteis produced. Still another object of the invention is that the methodcan be carried out in a relatively short time. The present inventiontherefore relates to a method for treating samples in a sealablecontainer, such as that described above, in which method the temperatureof the coolant is lower than 5° C. and a vessel is used which isprovided with an insulating material which is transparent toelectromagnetic radiation.

If a coolant at a low temperature is used, this has the advantage thatduring the heating of the sample and the polar non-solid medium nobuild-up of high pressures will occur since the heat of condensation caneffectively be removed and substances which are in the gas phase caneasily be returned again to the liquid or solid state, whereas thesample and the polar non-solid medium can be heated to a hightemperature. This is advantageous, in particular, if the processing iscarried out on a small scale using a device suitable therefor, as willbe clear to the person skilled in the art.

According to the invention, the method is suitable for treating sampleswhich have to undergo a heat treatment in the presence of a polarnon-solid medium. It is also possible that the polar non-solid mediumreacts with the sample or with one or more constituents thereof. Thus,for example, metals present in the sample may be reacted with a solutionof an acid in water to form the corresponding salts. Examples oftreatments in which samples undergo a heat treatment in the presence ofa polar non-solid medium are heating with reflux cooling, distillationor (continuous) extraction.

According to the invention, all kinds of samples can be treated by themethod. Examples of suitable samples are soil samples, samples ofsediments, sludge, minerals, oil and oil products, biological samples,samples containing metals and/or ceramic materials, and water samples,for example samples of surface water.

The temperature of the coolant must be lower than the temperature of themixture of the sample and of the polar non-solid medium. Preferably, thetemperature of the coolant is at least 20° C., more preferably at least35° C. and, in particular, at least 75° C. lower than the temperature ofthe mixture. Because the mixture will generally be at a temperature ofapproximately room temperature (approximately 25° C.) or higher, thetemperature of the coolant is therefore at least lower than 5° C.,preferably lower than -10° C. and, in particular, lower than -50° C.

According to the invention, the coolant must be essentially orcompletely transparent to electromagnetic radiation. The coolanttherefore preferably has a dissipation factor of less than 10, inparticular of less than 5.

The dissipation factor of a substance is understood as meaning the ratioof the lowering of the permittivity of the substance as a consequence ofexposure to electromagnetic radiation, the lowering factor or lossfactor ε" to the permittivity ε of the substance:

Dissipation factor=tan δ=ε"/ε.

Here the lowering factor or loss factor ε" is a measure of the abilityof the substance to dissipate the electromagnetic energy.

Examples of suitable coolants are liquid nitrogen, liquid argon andsolid carbon dioxide. Suitable coolants can also be certain, generallynonpolar, organic substances which have been cooled to the desiredtemperature for the use thereof as coolant. Examples of such organicsubstances are alkanes and halogenated alkanes. According to theinvention, a solid coolant, and in particular solid carbon dioxide, ispreferably used.

According to the invention the polar non-solid medium may be a polarliquid or a mixture of different polar liquids. A polar liquid isunderstood here as meaning a liquid which has a permittivity ε at 25° C.of at least 2, preferably of more than 5, more preferably of more than10 and, In particular, of more than 50. Suitable polar liquids may beinorgaic or organic substances. Examples of suitable polar liquids areacetone, ethanol, water, butanone, acetonitrile and certain oils andfats. Water, in particular, is used as the polar non-solid medium.

The polar non-solid medium may also be a mixture of one or more polarand nonpolar liquids. If the polar non-solid medium comprises a polarand a nonpolar liquid, such a medium will usually be a two-phase system.These two phases can be mixed, for example, by means of a stirringdevice. The mixing of a mixture of a polar and a nonpolar liquid canalso be increased by a means suitable therefor, for example a dispersantor a phase-trafer catalyst, such as hexadecylammonium bromide.

The polar non-solid medium may contain additives which are possiblydissolved in the medium. Said additives may be chemical substances whichreact with the sample or with one or more constituents thereof. Thus,the additives may be acids which react with metals to form thecorresponding salts. The additives may also be dispersants oremulsifiers or other substances which increase the dissolution,dispersion or emulsification of the sample or of one or moreconstituents thereof in the medium. Examples of such agents aremonoesters and diesters of glycerol and fatty acids having long chainsor monoesters of glycol and fatty acids having long chains, detergentssuch as alkyl sulphonates or alkyl ethoxylates and phase-transfercatalysts such as hexadecylammonium bromide.

According to the invention, the polar non-solid medium may also be apolar liquid which may be in the superheated state. Under the influenceof microwave radiation, a liquid can be heated at atmospheric pressureto a temperature which is higher than the boiling point of the liquid atatmospheric pressure. Thus, it has been found that, with the aid ofmicrowave radiation, water can be heated at atmospheric pressure to atemperature of approximately 105° C. and acetonitrile even to atemperature of approximately 120° C.

According to the invention, the polar non-solid medium may also be apolar substance which may be in the supercritical state. The polarnon-solid medium may also comprise one or more polar and nonpolarsubstances which may be in the supercritical state. According to theinvention, substances can advantageously be used which have a criticaltemperature of up to 200° C. and a permittivity ε of at least 5 at 25°C. Preferably, such substances have a critical temperature ofapproximately 0° to approximately 150° C. Examples of such suitablepolar substances ame dimethyl ether, fluoromethane andmonochlorodifluoromethane. Although chlorofluorohydrocarbons such asmonochlorodifluoromethane are suitable coolants, these substances are,however, less preferred because of their supposed disadvantageouseffects an the environment. Examples of suitable nonpolar substances arecarbon dioxide ad pentane, According to the present invention, the polarnon-solid medium is preferably chosen from the group comprising polarliquids and polar substances which can be in the superheated orsupercritical state.

It will be clear that the container has to be filled with a certainquantity of the polar non-solid medium. Preferably, the container isnot, however, completely filled. According to the present invention, thecontainer is therefore advantageously filled with a quantity of 10 to90% by volume of the mixture of the sample and the polar non-solidmedium, in particular with a quantity of 20 to 40% by volume.

According to the invention, electromagnetic radiation can he used whichfalls within the frequency range of radio waves having an ultra-highfrequency and microwaves. The frequency of the electromagrneticradiation is therefore, according to the invention, preferably between 3MHz and 30 GHz, in particular between 30 MHz and 3 GHz.

Before the sample is processed according to the method of the presentinvention, the sample and the polar non-solid medium are advantageouslymixed for at least 15 minutes and preferably for at least 30 minutes inthe container using a vortex stirring device so that pressure build-upand foam formation will occur to a lesser extent during the processingof the samples by the method according to the present invention.

The method according to the present invention is suitable, inparticular, for processing samples in this way which contain heavymetals, said heavy metals being dissolved with the aid of an acid, forexample a mixture of concentrated nitric acid and concentratedhydrochloric acid.

The invention also relates to a device for processing samples, whichcomprises a source of electromagnetic radiation, a vessel for a coolant,which vessel is transparent to electromagnetic radiation and a sealablecontainer, the source of electromagnetic radiation being placed outsidethe container and the container being placed inside the coolant and thevessel being provided with an insulating material which is transparentto electromagnetic radiation.

As described above, if a coolant is used at a low temperature, it isnecessary to use a vessel which is provided with an insulation materialso that condensation of water vapour on the wall of the vessel will notoccur and heating of the sample and the polar non-solid medium can takeplace efficiently in the container.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows an embodiment of the inventive apparatus.

FIGS. 2 and 3 show embodiments of the container.

FIG. 4 is a diagammatic example of an embodiment.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 1 shows an embodiment of the device according to the invention.Said embodiment comprises a source of electromagnetic radiation 11, acoolant 12 which is transparent to electromagnetic radiation, a sealablecontainer 13 and a vessel 14 which is transparent to electromagneticradiation and which is provided an the outside with an insulationmaterial which is transparent to electromagnetic radiation. It will beclear that the vessel can be composed largely or completely of aninsulation which is transparent to electromagnetic radiation.

The source of electromagnetic radiation is placed outside the containerand the container is placed inside the coolant. It is therefore possiblethat a source of electromagnetic radiation is used which is situatedoutside the container, but inside the vessel. A source ofelectromagnetic radiation can also be used with the source being placedoutside the vessel, provided that a vessel is used which is essentiallytransparent to electromagnetic radiation.

Preferably, the source of electromagnetic radiation provides radiationhaving a frequency of 3 MHz to 30 GHz, in particular of 30 MHz to 3 GHz.

The vessel 14 is provided with an insulating material so thatcondensation of water vapour is prevented from taking place on the wallof the vessel. It will be clear that the insulating material must beessentially transparent to electromagnetic radiation if the source ofelectromagnetic radiation is placed outside the vessel. The insulatingmaterial must also have suffficient insulating power to keep thecoolants sufficiently cool, said coolants being optionally enclosed by avessel, even if the temperature of the coolants is very low. Accordingto the invention, the insulating material preferably has a thermalconductivity of at most 0.1 W.m⁻¹.K⁻¹ at 24° C. and a dissipation factorof less than 100. Suitable insulating materials are plastics, forexample expanded polystyrene and polyurethane foam, glass wool, rockwool and certain ceramic materials, for example porcelain, alumina andcordenite.

The container 13 is advantageously resistant to aggressive chemicalsubstances, such as strong acids and bases. The container is thereforeadvantageously made of an essentially chemically inert material. Thematerial of which the container is made should also essentially betransparent to electromagnetic radiation. Suitable materials are, forexample, ceramic materials, glass and plastics. Suitable ceramicmaterials are porcelain, alumina and cordenite. Suitable types of glassare quartz, flint glass, pyrex and borosilicate. Suitable plastics are,for example, poly(tetrafluoroethene), polypropene, polystyrene,poly(sulphone), polyethene, polypropene, acrylamide/butadiene/styreneterpolymers and polycarbonate. The plastics may optionally be reinforcedwith fibres, for example fibre-reinforced epoxy resins. Examples ofsuitable fibres are glass fibres, carbon fibres and aramid fibres.

The container may optionally be made in such a way that it can withstandhigh and low pressures, for example pressures of 10⁻⁶ mbar to 150 bar.In addition, either an open container or a sealed container can be used.

The device according to the invention can also be provided with meansfor measuring and regulating the temperature of the mixture of thesample and the polar non-solid medium. Optionally, the device alsocomprises a means of measuring and regulating the pressure in thesealable container. The device is advantageously provided with a meanswhich regulates the power of the source of electromagnetic radiation. Itwill be clear that the device may be provided with more than one sourceso that electromagnetic radiation having different frequencies can besupplied. It is very advantageous if the device according to theinvention is provided with a means which regulates the power andoptionally the frequency of the electromagnetic radiation on the basisof the desired temperature of the polar non-solid medium.

According to the invention, the container may have diverse shapes. Apreferred embodiment of the container is shown in, FIG. 2. The container21 shown there is tubular and is provided at the top with a sealingmeans 22. The dimensions of the container are preferably: height 0.5 to50 cm, cross section 0.3 to 10 cm. The means 22 may seal the container21 by means of a screw joint, for example a screw thread joint or aso-called bayonet catch, or a quick-acting or snap joint. The means 22may also be provided with a means on which a supply device can bemounted by means, for example, of a screw thread joint. The means 22 mayalso comprise a means through which the supply device can be provided,for example a septum, through which an injection needle can be inserted.Such an embodiment of a device according to the invention is suitable,in particular, for carrying out chemical reactions because one or morereagents can be added while the method according to the invention isbeing carried out.

The preferred embodiment according to FIG. 2 may also be provided with amaterial which is essentially opaque to electromagnetic radiation sothat only the sample and the polar non-solid medium can be exposed toelectromagnetic radiation in the course of the method according to theinvention. The material which is essentially opaque to electromagneticradiation is therefore mounted on the outside and/or the inside of thewall of the container in such a way that the material which isessentially opaque to electromagnetic radiation is mounted between means22 and the level of the sample and the polar non-solid medium. In thisconnection, it is, however, necessary for the length of the materialwhich is essentially opaque to electromagnetic radiation not to be suchthat it can act as an aerial for the electromagnetic radiation. Thelength of the material should therefore not be equal to a whole multipleof the half wavelength of the electromagnetic radiation.

Preferably, the material which is opaque to electromagnetic radiationcontains one or more metals and said material is, in particular, analuminium-containing foil.

Another preferred embodiment of the container is shown in FIG. 3. Saidpreferred embodiment is a so-called (inverted) u-shape and comprises twoupright tubular parts 31 and 32, the upright tubular parts being joinedby a transversely situated tubular part 33. The various parts mayoptionally be separable. The dimensions of said preferred embodimentare: height 0.5 to 50 cm, width 0.5 to 25 cm, cross section of the parts31-33 0.3 to 10 cm. The container is optionally also provided with oneor more sealable openings for filling and emptying it. Such anembodiment of the container is suitable, for example, for carrying out adistillation. In this connection, for example, tubular part 31 is filledwith a mixture of liquids and the container is placed in the coolant.Then the container is irradiated in such a way that only the tubularpart 31 is exposed to electromagnetic radiation, as a result of whichvapour of the most volatile liquid(s) will condense in the tubular part32. It will be clear that the partial irradiation of the container canbe carried out when the entire container is exposed to electromagneticradiation, the tubular part 32 being shielded by a material whichessentially transmits no electromagnetic radiation, said materialpreferably being the same as the material which is essentially opaque toelectromagnetic radiation and which can be used in the exemplaryembodiment according to FIG. 2.

It goes without saying that a container can also be used which is anassembly of more tubular parts and one or more parts may be straight orcurved. It is therefore possible to use containers which have a complexgeometry. Examples of such containers which have complex geometry arecomparable with apparatuses for carrying out extractions anddistillations, for example a soxhlet extraction apparatus (solid/liquidextraction).

The container can be exposed to electromgnetic radiation in such a waythat only some of the coolant or of the vessel containing the coolant isirradiated. A container will advantageously be only partially exposed toelectromagnetic radiation if it comprises more tubular parts, inparticular if a container is used which is suitable, for example, forcontinuous extraction.

A diagrammatic example of such an embodiment, which is optionallyseparable, for carrying out a continuous extraction is shown in FIG. 4.Said embodiment comprises two upright tubular parts 41 and 42 and twotransversely situated parts 43 and 44, part 44 being provided with asealing means 45. In this case, part 44 acts as a siphon. Part 41 alsocomprises a tube 46. Such an embodiment can, for example, be used asfollows. Part 41 is filled with a mixture of a suitable polar liquidwhich contains substances which it is desired to extract, and a suitablenonpolar liquid, the nonpolar liquid having a lower density than thepolar liquid. Part 41 is filled with the mixture to a level below thatof part 44 so that the tube 46 projects into the polar liquid. Part 42is filled with the nonpolar liquid to a level below that of part 44. Thecontainer is placed in the coolant.

The operation of this embodiment is as follows. If part 42 is exposed toelectromagnetic radiation, nonpolar liquid will evaporate and condensein part 41, as a result of which nonpolar liquid is passed through thepolar liquid via tube 46. During the process, the level of the nonpolarliquid rises in part 41. Ultimately, the level reaches the height of, orhigher than, part 44, as a result of which some of the nonpolar liquidcontaining the extracted substances can be siphoned back into part 42 byopening sealing means 45. Ultimately, almost all the extractedsubstances will be contained in part 42. After completing the continuousextraction, the content of part 41, i.e. the combination of the polarliquid and some of the nonpolar liquid may optionally be separated inorder to obtain the last residues of substances to be extracted.

The invention will be explained further by reference to an example.

EXAMPLE I

In this example, two methods for preparing the sample (digestion) aredescribed, method A corresponding to the method according to theinvention and method B and C Comprising a standard procedure.

The contents of different metals (cadmium, chromium, copper, nickel,lead, zinc, arsenic and mercury) in different soil samples aredetermined by treating the soil samples with a mixture of nitric acidand hydrochloric acid and then analysing the dissolved salts of saidmetals with the aid of ICP.

Method A (according to the invention; derived from NVN 5770):

A quantity of 0.15 to 0.4 g of visually homogeneous samples having acontent of solids of more than 50% by weight was weighed out with anaccuracy of 0.0001 g into a disposable polypropylene conical-bottom tube(14 ml, 17×200 mm). Then 1.9 ml of a hydrochloric acid solution preparedby adding 50 ml of demineralized water to 2.5 1 of concentratedhydrochloric acid (12 mol HCl per litre), and 0.6 ml of a nitric acidsolution (15 mol of HNO₃ per litre) were added to the weighed quantitiesof the samples. The conical-bottom tube was then sealed with a screwlid.

The conical-bottom tubes were shaken with the aid of a vortex stirringdevice until carbon dioxide no longer escaped and/or other visiblereactions no longer took place; it is found that shaking for at least 30minutes is generally adequate.

In a subsequent step, 10 conical-bottom tubes were placed with a gap ofat least 1 cm in an expanded polystyrene tray completely filled withsolid carbon dioxide in such a way that the conical-bottom tubes wereclear of each other and clear of the wall of the tray. The tray was thensealed with a lid.

The tray was then placed in a microwave oven (MDS 2000 from CEMCorporation) and subjected to the following program;

Power: 23%

Time: 60 minutes

Fan speed; 100 rpm.

After removing them from the tray, the tubes were allowed to cool toroom temperature and 11.5 ml of demineralized water was added to eachtube, a final volume of 14.0 ml being obtained.

The content of the conical-bottom tubes was homogenized and the solidmaterial was allowed to settle or the tubes were centrifuged.

Then a 1.0 ml sample was taken from the conical-bottom tubes foranalysis for mercury, said sample being introduced into a 12 mlconical-bottom tube (17×150 mm). Then 9.0 ml of demineralized water wasadded and the content of the conical-bottom tube was homogenized.

Method B (comparative):

This method was carried out in accordance with the standardized methodNEN 6465 and comprises a digestion using a conventional laboratoryset-up (reflux condenser).

Method C (comparative):

This method was carried out in accordance with the standardized methodNVN 5770, the digestion being carried out in a Teflon vessel usingmicrowaves.

The quantities of cadmium, chromium, copper, nickel, lead, zinc, arsenicand mercury in the samples pretreated according to method A, B or C weredetermined with the aid of ICP. The results were evaluated with the aidof a statistical test [Wilcoxon-T test; D. L. Massart, B. G. M.Vandeginste et al., "Chemometrics: A Textbook", Vol. 2, "Data Handlingin Science and Technology", pages 57-58 (1988)]. This test is atwo-sided check for the differences in paired observations. having anuncertainty of 0.05.

From the results of this test, a quantitative evaluation can be drawn upwhich is shown in the table below, the degree of certainty beingindicated by evaluation FIGS. 1-5. In this connection, the evaluationFIG. 1 indicates a low certainty and the evaluation FIG. 5 a highcertainty. A difference between two evaluation figures of 2 or more isstatistically significant. An evaluation figure of 1 is assigned to theleast certain method, the evaluation figures of other methods beingincreased by 1 (more reliable, not statistically significant) or by ormore (more reliable, statistically significant).

    ______________________________________                                        Method A         Method B Method C                                            ______________________________________                                        Cd    4              3        1                                                 Cr 3 5 1                                                                      Cu 2 2 1                                                                      Ni 2 3 1                                                                      Pb 3 1 2                                                                      Zn 2 4 1                                                                      As 3 1 2                                                                      Hg 4 1 3                                                                    ______________________________________                                    

From the above table it is apparent that the comparative method C yieldsthe least reliable results for the elements cadmium, chromium, copper,nickel and zinc. The least reliable results are obtained by method B forthe elements lead, arsenic and mercury. The method according to theinvention (method A) therefore yields the most reliable result for theseries of elements which are shown in the above table so that thismethod is preferable for such an analysis. A further advantage of themethod according to the invention is that simple equipment and onlysmall quantities of various chemicals are needed.

What is claimed is:
 1. Method for processing samples in a sealablecontainer which is transparent to electromagnetic radiation, in whichmethod:a) the sample and a polar liquid medium are introduced into thecontainer, b) the container is placed in a vessel which is transparentto the electromagnetic radiation and which is filled with a nonpolarcoolant which is transparent to the electromagnetic radiation, and c)the vessel is irradiated with electromagnetic radiation, wherein thefrequency of the electromagnetic radiation is between 3 MHz and 30 GHz,wherein the temperature of the coolant is maintained lower than 5° C. toprovide for condensation of gaseous products formed in the containerupon heating and wherein a vessel is used which is provided with aninsulating material which is transparent to the electromagneticradiation.
 2. Method according to claim 1, wherein the liquid coolanthas a dissipation factor of less than
 10. 3. Method according to claim1, wherein the coolant is a solid coolant.
 4. Method according to claim3, wherein the coolant is solid carbon dioxide.
 5. Method according toclaim 4, wherein the polar liquid medium is chosen from the groupcomprising polar liquids and polar substances which are in thesupercritical state.
 6. Method according to claim 1, wherein thecontainer is filled with a quantity of 10-99% by volume of the mixtureof the sample and the polar liquid medium.
 7. Method according to claim1, wherein the container is filled with a quantity of 20-40% by volumeof the mixture of the sample and the polar liquid medium.
 8. Methodaccording to claim 1, wherein a U-shaped container is used whichcomprises two upright tubular parts which are joined by a transverselysituated tubular part wherein the tubular parts are optionallyseparable.
 9. Method according to claim 1, wherein the coolant isirradiated with electromagnetic radiation in such a way that only a partof the container is exposed to electromagnetic radiation.
 10. Methodaccording to claim 1, wherein a container is used which is provided witha material which is opaque to electromagnetic radiation in such a waythat, in step c), only the sample and the polar liquid medium areexposed to electromagnetic radiation.
 11. Method according to claim 10,wherein a length of the material which is essentially opaque toelectromagnetic radiation is not equal to a whole multiple of the halfwavelength of the electromagnetic radiation.
 12. Method according toclaim 10, wherein the material which is opaque to electromagneticradiation contains one or more metals.
 13. Method according to claim 12,wherein the material which is opaque to electromagnetic radiation is analuminium-containing foil.
 14. Method according to claim 1, wherein onlythat part of the container is cooled which is in contact with the sampleand the polar liquid medium.
 15. Device for processing samples, whichcomprises a source of electromagnetic radiation wherein the source ofelectromagnetic radiation supplies radiation at a frequency of 3 MHz to30 GHz, a vessel for a coolant, which vessel is transparent toelectromagnetic radiation, and a sealable container, the source ofelectromagnetic radiation being placed outside the container and thecontainer being placed inside the coolant, the vessel is provided withan insulating material which is transparent to electromagneticradiation.
 16. Device according to claim 15, wherein the thermalconductivity of the insulating material is at most 0.1 W.m⁻¹ .K⁻¹ at 24°C.
 17. Device according to claim 15, wherein the dissipation factor ofthe insulating material is less than
 100. 18. Device according to claim15, wherein the container is provided with a material which isessentially opaque to electromagnetic radiation in such a way that, ifthe container contains a sample and a polar liquid medium, only thesample and the polar liquid medium can be exposed to electromagneticradiation.
 19. Device according to claim 18, wherein the length of thematerial which is essentially opaque to electromagnetic radiation is notequal to a whole multiple of the half wavelength of the electromagneticradiation.
 20. Device according to claim 19, wherein the material whichis opaque to electromagnetic radiation contains one or more metals. 21.Device according to claim 20, wherein the material which is opaque toelectromagnetic radiation is an aluminium-containing foil.
 22. Deviceaccording to claim 15, wherein the container is made of a chemicallyinert material.
 23. Device according to claim 15, wherein the chemicallyinert material may be a ceramic material, glass or a plastic.
 24. Deviceaccording to claim 15, wherein the container is a u-shaped containercomprising two upright tubular parts which are joined by a transverselysituated tubular part, wherein the tubular parts are optionallyseparable.
 25. Method of claim 1, wherein said step of placing acontainer in a vessel, places a container without a separatereinforcement means for resisting high pressures with the container.